Revolving tower cranes are put up and taken down very frequently. In this respect, the required precautions have to be taken so that an appropriate safety level is ensured; the required stability of the crane should in particular be ensured.
The monitoring of the stability of a crane currently takes place in a known manner by measuring secondary values at the crane. In this respect, a torque is monitored that is a consequence of the loading of the crane with a load torque. All other influences are not considered. These influences are, for example, errors in the putting up of the crane, e.g. when it is incorrectly leveled, settling of the substructure, tolerances in putting up the tower, wind, etc.
To determine the inclination of the crane, it is as customary in excavating machines or in mobile cranes to use tilt sensors that are very robust and precise and that serve either to monitor the stability of the machine or to improve the quality of the work to be carried out. The position of the upper crane with respect to the tower system and to the substructure is, however, not taken into account at all.
It is customary to use square tower systems. The stability is only identical in individual points in this respect. An apparatus is provided in a known manner for a continuous determination of the stability having four observation points spaced apart from one another, said apparatus having devices for detecting values decisive for the stability. These devices forward the detected values to a comparison device for comparison with previously determined maximum permitted values or switch off directly. On an exceeding of a predefined fixed value at an observation point, a monitoring signal is output that indicates that the stability is no longer present. The stability changes on a rotation of the crane.
The currently used systems thus only take account of a defined and maximum stability without considering the position of the upper crane. Situations on the putting up of the crane are furthermore currently excluded from the monitoring, which could have devastating consequences on the putting up. The monitoring of the stability only starts after the crane has been put up in known systems. Situations also arise in use that are not currently detected, e.g. settling in the substructure or damage.